Many machines, particularly earth working machines, use a hydrostatic drive system to drive the traction wheels or tracks of the machine. Frequently, the prime mover engine of the machine is set to operate at a predetermined speed via an engine throttle. The machine speed can then be regulated by controlling the displacement of one of the hydraulic elements of the hydrostatic drive system, without adjusting the engine throttle.
One problem common to many known hydrostatic drive systems is that operation of the hydraulic elements produce loads on the engine that causes engine "stalling" or "lugging", a.k.a., excessive engine speed droop; thereby causing the decreased productivity of the machine. For most machines, the operator is required to control the engine load manually by controlling the displacement of the hydraulic elements. However, this is tedious and often difficult. For other machines, electronic controllers are used to control the displacement of the hydraulic elements in response to engine speed. However, many of such systems become unstable because the time required to make necessary adjustments to the hydraulic elements is much greater that the time necessary to generate a command signal in response to changes in engine speed.
The present invention is directed to overcoming one or more of the problems as set forth above.